1. Field of the Invention
The present invention relates to a novel method and additive as well as a method for making the additive which is useful for improving the gelation property of fish meat. More particularly, the present invention is concerned with improving the gelation of fish meat paste products in instances where the fish meat is obtained from fish which are contaminated with certain types of sporozoa. Fish meat which is contaminated or infected with these sporozoa parasites have a propensity for becoming soft and the softened condition prevents the gelation of certain fish meat paste products in which gelation is a highly desirable feature. The invention is also concerned with improving the gelation of fish meat which is obtained from certain species of fish which are not contaminated with the sporozoa but which become soft when processed into fish meat paste products but to a lesser degree than those contaminated with sporozoa.
2. Background Information and Description of Related Art
The muscle tissue of several species of fish are infected with myxosporea parasites. It is known that the proteolytic enzyme activity associated with these parasites causes the fish which are contaminated with these parasites to develop the so-called "softened condition" in which the fish meat is spottily or wholly softened and/or liquefied. This softened condition interferes with the processing of the fish meat into certain paste-like products wherein the formation of a firm gel having adequate elasticity is highly desirable. These paste products include surimi, neriseihin, kamaboko and related products such as those described in U.S. Pat. Nos. 4,284,653 and 4,207,354; the specifications of which are incorporated herein by reference.
In making the fish meat paste products, a kneaded meat is prepared from the fish muscle. When the kneaded meat is prepared from fish meat having the tendency to become soft, the kneaded meat exhibits no gel-forming capability or a greatly reduced gel-forming capability and thereby remains in a non-gelled soft condition after heating.
It has been noted that because of the proteolytic enzyme(s) activity associated with these parasites, some softness or lack of texture can occur during storage of contaminated fish under un-iced or even iced conditions prior to freezing. In addition, it has been noted by Tsuyuki et al. in the Fisheries and Aquatic Sciences, Canadian Technical Report #1130 (1982) that the texture can be completely lost during slow heating since the enzyme(s) have been known to be active over a rather wide temperature range (20.degree.-75.degree. C.). Since these temperature ranges must be traversed during normal heating and cooking of such infected fish, mushiness can occur and the fish is unacceptable for normal consumer uses.
Pacific whiting, Merluccius productus, is one of the species commonly infected with myxosporea. The parasite problem has lead to low economic value and the lack of utilization of this abundant resource. Due to the difficulty in spotting infected versus non-infected fish or fillets, it is not practical to try to segregate and discard infected fish. Also, the level of infestation varies and so does the degree of softening between various lots of fish. Therefore, one can see that producing a consistent product from the muscle of Pacific whiting is difficult without some means of providing insurance against this degradation. Several workers have suggested that rapid heating during cooking might provide a solution by quickly exceeding the active temperature range and destroying the enzyme before it can act. However, this has not proven to be a practical solution.
Because the myxosporea parasites Kudoa thyrisitis and Kudoa paniformis are intra-muscular in their distribution, it is believed that a salt solubilization step is required to gain access to the enzyme. This was demonstrated by Niki et al. in the Bull. Jap. Soc. of Sci. Fish.; Vol. 50; pp 2043-2047 (1984). Niki attempted to remove the proteolytic enzyme(s) from Peruvian whiting (also infected by the same myxosporea parasite as Pacific whiting) by water washing. Continual washing of minced flesh of Peruvian hake did not result in removal of the enzyme(s), as shown by the lack of gelling properties of kamboko made from the water-washed muscle. However, the addition of salt following the last wash (more than 0.45 M NaCl) followed by a period of mixing and subsequent dilution with water, allowed the myofibrillar proteins to settle out of solution while the enzyme remained in solution. Recovery of these myofibrillar proteins by separating them from the water (which now contained the enzyme released by the salt solubilizing step) provided a functional protein which made a kamaboko of respectable gel-strength and elasticity. This demonstrated that a salt solubilizing step was needed somewhere in the process to gain access to the enzyme within the muscle fibers. Earlier workers (Konagaya and Oaki, Bull. Tokai Reg. Fish. Res. Lab. No. 105, October, 1981) had concluded that the enzyme(s) was derived from the parasite and was in the muscle fibers of infected Pacific whiting.
The functional properties of surimi are derived after salt solubilizing the proteins by kneading the surimi with salt. Flavorings, starches, and other ingredients are added, the product is formed or shaped, and then heat set into a gel. Addition of a specific inhibitor at the time one solubilizes the surimi by mixing with salt should provide an effective deterrent to protease enzyme degradation upon heating. Alternatively the inhibitor can be added at the time cryoprotectants are mixed with the refined mince to make surimi prior to freezing of surimi.
Several researchers have demonstrated that the enzyme(s) responsible for softening muscle in Pacific whiting is of the thiol type.
Haga et al. (1984) in U.S. Pat. No. 4,207,354 describes the addition of egg white to myxosporea-contaminated fish meat to allow it to be processed into a coagulated fish paste. Essentially they added egg white which contains proteolytic enzyme inhibitors at either the surimi making stage or at the kamaboko making stage which allowed them to produced a coagulated fish paste. These authors concluded that the addition of 3% egg white to Pacific whiting surimi made a very satisfactory kamaboko. However. 0.5-6.0% dried egg white is a very expensive ingredient and at higher levels imparts a definite undesirable egg-like odor to the final product.
Nagahisa et al. (Bull. Jap. Soc. Sci. Fish., 49(6); 901-906; 1983) blended flesh prepared from frozen Pacific whiting with Alaska pollock surimi and compared several additives with respect to their effect on gel-strength. Among the additives tested was a freeze-dried water extract of potato which had some effectiveness when added at the 1% level. Nagahisa et al. reported they used 1% of a freeze-dried water extract of potato and achieved moderate results for inhibition of the enzyme and preservation of gel-strength in a mixture of Pacific whiting meat and Alaska pollock surimi. However, these authors neglected to say that you cannot make a water extract from raw potatoes (Solanum tuberosum) and freeze dry this material without the product turning nearly black or dark purple in color. This imparts an objectionable dark gray color to the kamaboko even when added to surimi at low levels of 1% or even less. This approach is unsatisfactory since all the soluble components of the potato are very reactive and quickly discolor prior to freezing and freeze-drying.
In addition to fish which are contaminated with myxosporea parasites, it has been observed that meat of certain species of fish have a lower gel-strength in many cases without exhibiting a soft condition even though causative parasites are absent. For example, the meat of Alaska pollock in some cases is known to vary in gel-strength when made into kamaboko type products, yet these fish are not infected with myxosporea parasites. Thus, the cause of this is unrelated to the parasitic induced softening observed with respect to myxospora contaminated fish. Therefore, a need still exists in the art to treat uninfected fish to improve the gel characteristics of the meat products made therefrom. It would also be highly desirable to improve upon the methods and compositions used to treat myxosporea infected fish to avoid the development of the softened condition and to improve the gel quality of the fish paste product made therefrom.